The present invention relates to a shroud integral type moving blade and a split ring of a gas turbine which can prevent the leakage flow of a gas path (combustion gas main flow). It is noted that xe2x80x9cblade midpointxe2x80x9d indicates a certain position from the leading edge of a blade to the trailing edge thereof in this specification.
Generally, a gas turbine consists of a casing, a rotor which is attached rotatably to the casing, a plurality of stationary blades which are annularly arranged in the casing, and a plurality of moving blades which are annularly arranged in the rotor. The gas turbine produces power by the rotation of the moving blades and the rotor when combustion gas passes through the stationary blades and the moving blades.
A shroud integral type moving blade and a split ring of the gas turbine will be explained in detail with reference to FIGS. 17 and 18.
In FIG. 17, reference symbol 1 denotes a shroud integral type moving blade. The shroud integral type moving blade 1 is constituted so that a plate shroud (a tip shroud or a shroud cover) 3 is provided integrally with the tip of a moving blade 2. In FIG. 17, the shroud integral type moving blade 1 is on a rear stage side, e.g., in the third or fourth stage.
An inner side surface 4 of the shroud 3 is inclined along a gas path 5 which is indicated by an arrow of a solid line in FIG. 17. Namely, the radius of the inner side surface 4 of the shroud 3 (radius from the rotary shaft of the rotor) gradually increases from the upstream side of the gas path 5 to the downstream side thereof.
A seal fin 7 is provided integrally on an outer side surface 6 of the shroud 3. As shown in FIG. 18, the seal fin 7 is extended in the rotation direction of the shroud integral type moving blade 1 (indicated by a blank arrow in FIG. 18). In addition, the adjacent shrouds 3 are provided to be continuous to each other, whereby the seal fin 7 is shaped into a ring in the rotation direction of the shroud integral type moving blade 1. The ring-shaped seal fin 7 seals the outer side surface 6 of the shroud 3 from the flat inner peripheral surface 12 of a split ring 10 to be explained later, while facing the flat inner peripheral surface 12 of the split ring 10.
Contacts 8 are provided integrally on both ends of (the seal fin 7 of) the shroud 3, respectively. A contact surface 9 is provided on the outer side surface of each contact 8. As shown in FIG. 18, the contact surfaces 9 of the adjacent shrouds 3 frictionally abut on each other, whereby the shrouds 3 are provided continuous to each other.
The shroud integral type moving blade 1 functions as follows.
1. The sealing function of the seal fin 7 decreases pressure loss and leakage flow rate caused by the clearance between the blade 1 and the flat inner peripheral surface 12 of the split ring 10.
2. The reinforcing function of the shroud 3 integral with the tip of the moving blade 2 increases characteristic frequency and improves vibration intensity.
3. The function of the frictional abutment of the contact surfaces 9 enables increasing vibration damping.
In FIG. 17, reference symbol 10 denotes a split ring. The split ring 10 is arranged on the casing side to support stationary blades. The inner peripheral surface 11 of the split ring 10, similarly to the inner side surface 4 of the shroud 3, is inclined along the gas path 5. A part 12 on the inner peripheral surface 11 of the split ring 10, which faces the shroud integral type moving blade 1 is of a flat shape recessed outward.
In recent years, gas turbines which ensure high turbine efficiency and which have large capacity have been mainly employed. It, therefore, becomes necessary to increase work responsible for each blade of each step and the distance from the rotary shaft of the rotor to the tip of each moving blade (the radius of the tip of the moving blade) tends to be longer. Accordingly, a higher bending stress resulting from a centrifugal force acts on the shroud 3 of the shroud integral type moving blade 1.
As a result, it is necessary to suppress the high bending stress resulting from the centrifugal force and acting on the shroud 3 to an allowable value or below. To this end, the shroud 3 is cut from a state indicated by a two-dot chain line into a state indicated by a solid line (to have a winglet shape) so as to make the shroud 3 lighter in weight as shown in FIG. 18.
Nevertheless, if the shroud 3 is cut into a winglet shape, a void 14 is formed near a throat 13 after cutting the shroud 3 as shown in FIG. 18. This void 14 ranges widely as shown in FIG. 18.
Meanwhile, a large cavity cross-sectional area 15 (portion indicated by a two-dot chain line in FIG. 17) is formed between the outer side surface 6 of the shroud 3 and the flat inner peripheral surface 12 of the split ring 10 on the downstream side of the seal fin 7 in the conventional shroud integral type moving blade 1 and the conventional split ring 10.
Because of the large cavity cross-sectional area 15, leakage flows 16 and 17 (indicated by arrows of broken lines in FIGS. 17 and 18) occur from the gas path 5 in the conventional shroud integral type moving blade 1 and split ring 10, as shown in FIGS. 17 and 18.
The leakage flow 16, in particular, slips out of the gas path 5 through the void 14 near the throat 13, temporarily enters the cavity 15 between the shroud 3 and the split ring 10 and joins again with the gas path 5 from the cavity 15. On the other hand, the leakage flow 17 temporarily enters between the shroud 3 and the split ring 10 from the gas path 5. However, the leakage flow 17 is shut off by the seal fin 7.
As can be seen, much pressure loss occurs to the conventional shroud integral type moving blade 1 and split ring 10 since the leakage flow 16 interferes and mixes with the gas path 5. In addition, the leakage flow 16 shifts the efflux angle of the moving blade 2 (throat area S, see FIG. 3) from a design value. If the efflux angle is shifted from the design value, a pressure ratio and the degree of reaction are shifted from respective design values, resulting in the deterioration of efficiency.
It is an object of this invention to provide a shroud integral type moving blade and a split ring of a gas turbine which can prevent the leakage flow of a gas path.
The gas turbine according to one aspect of this invention comprises the shroud integral type moving blade and the split ring. The shroud integral type moving blade has a structure in which a shroud is provided from a leading edge of a tip of a moving blade to a trailing edge of the tip of the moving blade, and in which a radius of a seal fin tip end is substantially equal to a radius of a trailing edge of the shroud. The split ring has a structure in which a radius of its inner peripheral surface is slightly larger than a radius of the seal fin tip end and the radius of the trailing edge of the shroud to prevent a leakage flow of a gas path.
The gas turbine according to another aspect of this invention comprises the shroud integral type moving blade and the split ring. The shroud integral type moving blade has a structure in which a shroud is provided from a leading edge of a tip of a moving blade to a trailing edge of the tip of the moving blade, in which a flat section is provided on a trailing edge of the shroud and in which a radius of a seal fin tip end is substantially equal to a radius of the trailing edge of the shroud. The split ring has a structure in which a radius of its inner peripheral surface is slightly larger than a radius of the seal fin tip end and a radius of the flat section to prevent a leakage flow of a gas path.
The gas turbine according to still another aspect of this invention comprises the shroud integral type moving blade and the split ring. The shroud integral type moving blade has a structure in which a shroud is provided from a leading edge of a tip of a moving blade to halfway along a trailing edge of the tip of the moving blade, in which a flat section is provided on the trailing edge of the tip of the moving blade and in which a radius of a seal fin tip end is substantially equal to a radius of the flat section on the trailing edge. The split ring has a structure in which a radius of its inner peripheral surface is slightly larger than the radius of the seal fin tip end and the radius of the flat section on the trailing edge of the tip to prevent a leakage flow of a gas path.
The gas turbine according to still another aspect of this invention comprises the shroud integral type moving blade and the split ring. The shroud integral type moving blade has a structure in which a radius of a seal fin tip end is larger than a radius of a tip side of a shroud and a radius of a tip side of a moving blade. The split ring has a structure in which a step section is provided from a portion which faces the seal fin to a downward portion, in which a radius of an inner peripheral surface of the step section is slightly smaller than a radius of an inner peripheral surface of the portion which faces the seal fin and slightly larger than a radius of the tip side of the shroud and a radius of the tip side of the moving blade to prevent a leakage flow of a gas path.
The gas turbine according to still another aspect of this invention comprises the shroud integral type moving blade and the split ring. The shroud integral type moving blade has a structure in which a shroud is provided from a leading edge of a tip of a moving blade to a midpoint of the tip of the moving blade, in which a seal fin is provided at the midpoint of the tip of the moving blade, in which a flat section is provided from the midpoint of the tip of the moving blade to a trailing edge of the tip of the moving blade, and in which a radius of a seal fin tip end is substantially equal to a radius of the flat section. The split ring has a structure in which a radius of its inner peripheral surface is slightly larger than the radius of the seal fin tip end and the radius of the flat section to prevent a leakage flow of the gas path.
The gas turbine according to still another aspect of this invention comprises the shroud integral type moving blade and the split ring. The shroud integral type moving blade has a structure in which a shroud is provided from a leading edge of a tip of a moving blade to a midpoint of the tip of the moving blade, in which a seal fin is provided at the midpoint of the tip of the moving blade, in which a flat section is provided from the midpoint of the tip of the moving blade to a trailing edge of the tip of the moving blade, and in which a radius of a seal fin tip end is larger than a radius of the flat section of the tip. The split ring has a structure in which a step section is provided from a portion which faces the shroud to a downward portion, in which a radius of an inner peripheral surface of the step section is slightly smaller than a radius of an inner peripheral surface of the portion which faces the shroud to prevent a leakage flow of a gas path.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.